java积累

数组的使用

package javaDemo;
import java.util.*;
/**
 *
 * @author Administrator
 * @version 1.0
 *
 *
 */
public class test {
    public static void main(String[] args)
    {
        String[] greeting = new String[3];
        greeting[0] = "Welcome to Core Java";
        greeting[1] = "by Cay Horstmann";
        greeting[2] = "and Gary Cornell";

        for (String g : greeting)
            System.out.println(g);
    }

}

eclipse格式化快捷键Ctrl+Shift+F

jFrame

package javaDemo;

/**
 *
 * @author Administrator
 * @version 1.0
 *
 *
 */
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;

/**
 * A program for viewing images.
 */
public class ImageViewer {
    public static void main(String[] args) {
        JFrame frame = new ImageViewerFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

/**
 * A frame with a label to show an image.
 */
class ImageViewerFrame extends JFrame {
    public ImageViewerFrame() {
        setTitle("ImageViewer");
        setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);

        // use a label to display the images
        label = new JLabel();
        add(label);

        // set up the file chooser
        chooser = new JFileChooser();
        chooser.setCurrentDirectory(new File("."));

        // set up the menu bar
        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);

        JMenu menu = new JMenu("文件");
        menuBar.add(menu);

        JMenuItem openItem = new JMenuItem("打开");
        menu.add(openItem);
        openItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                // show file chooser dialog
                int result = chooser.showOpenDialog(null);

                // if file selected, set it as icon of the label
                if (result == JFileChooser.APPROVE_OPTION) {
                    String name = chooser.getSelectedFile().getPath();
                    label.setIcon(new ImageIcon(name));
                }
            }
        });

        JMenuItem exitItem = new JMenuItem("退出");
        menu.add(exitItem);
        exitItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                System.exit(0);
            }
        });
    }

    private JLabel label;
    private JFileChooser chooser;
    private static final int DEFAULT_WIDTH = 400;
    private static final int DEFAULT_HEIGHT = 500;
}

BigIntegerTest

package javaDemo; //首先要引入包
/**
  * @version 1.20 2004-02-10
  * @author Cay Horstmann
  *
  **/

import java.math.*; //引入一些math相关的东西
import java.util.*;

public class BigIntegerTest //类名和文件名要相同
{
   public static void main(String[] args)  //主函数也就是入口函数
   {
      Scanner in = new Scanner(System.in); //键盘输入的对象

      System.out.print("How many numbers do you need to draw? ");
      int k = in.nextInt(); //获取数据，存入变量k中

      System.out.print("What is the highest number you can draw? ");
      int n = in.nextInt(); //获取数据，存入变量n中

      /*
         compute binomial coefficient
         n * (n - 1) * (n - 2) * . . . * (n - k + 1)
         -------------------------------------------
         1 * 2 * 3 * . . . * k
      */

      BigInteger lotteryOdds = BigInteger.valueOf(1);

      for (int i = 1; i <= k; i++)
         lotteryOdds = lotteryOdds
            .multiply(BigInteger.valueOf(n - i + 1))
            .divide(BigInteger.valueOf(i));

      System.out.println("Your odds are 1 in " + lotteryOdds + ". Good luck!");//进行一些处理
   }
}

稍微复杂的算法

package javaDemo; //首先要引入包
/**
   @version 1.40 2004-02-10
   @author CayHorstmann
*/

public class CompoundInterest
{
   public static void main(String[] args)
   {
      final int STARTRATE = 10; //定义常量
      final int NRATES = 6;
      final int NYEARS = 10;

      // set interest rates to 10 . . . 15%
      double[] interestRate = new double[NRATES]; //新建数组
      for (int j = 0; j < interestRate.length; j++)
         interestRate[j] = (STARTRATE + j) / 100.0; //给数组赋值

      double[][] balances = new double[NYEARS][NRATES]; //定义二维数组

      // set initial balances to 10000
      for (int j = 0; j < balances[0].length; j++)
         balances[0][j] = 10000;

      // compute interest for future years
      for (int i = 1; i < balances.length; i++)
      {
         for (int j = 0; j < balances[i].length; j++)
         {
            // get last year's balances from previous row
            double oldBalance = balances[i - 1][j];

            // compute interest
            double interest = oldBalance * interestRate[j];

            // compute this year's balances
            balances[i][j] = oldBalance + interest;
         }
      }

      // print one row of interest rates
      for (int j = 0; j < interestRate.length; j++)
         System.out.printf("%9.0f%%", 100 * interestRate[j]);

      System.out.println();

      // print balance table
      for (double[] row : balances)
      {
         // print table row
         for (double b : row)
            System.out.printf("%10.2f", b);

         System.out.println();
      }
   }
}

同一个包下可以互相引用类，并使用其中方法
CompoundInterest comp = new CompoundInterest();
comp.main(args);

package javaDemo; //首先要引入包
/**
   @version 1.10 2004-02-10
   @author Cay Horstmann
*/

import java.util.*;

public class InputTest
{
   public static void main(String[] args)
   {
      Scanner in = new Scanner(System.in);

      // get first input
      System.out.print("你叫什么名字? ");
      String name = in.nextLine();

      // get second input
      System.out.print("你多大了? ");
      int age = in.nextInt();

      // display output on console
      System.out.println("你好, " + name + ". 明年, 你的年龄将会是 " + (age + 1));
   }
}

如何调整console字体大小？

打开window - preferences-- general - appearance - colors and fonts --debug - console font 就可以调节了。

我表示看不懂，这算法太复杂了，工作这么久，都不懂。

package javaDemo;
/**
   @version 1.20 2004-02-10
   @author Cay Horstmann
*/

public class LotteryArray
{
   public static void main(String[] args)
   {
      final int NMAX = 5; //定义常量

      // allocate triangular array
      int[][] odds = new int[NMAX + 1][]; //定义数组
      for (int n = 0; n <= NMAX; n++)
         odds[n] = new int[n + 1];

      // fill triangular array
      for (int n = 0; n < odds.length; n++)
         for (int k = 0; k < odds[n].length; k++)
         {
            /*
               compute binomial coefficient
               n * (n - 1) * (n - 2) * . . . * (n - k + 1)
               -------------------------------------------
               1 * 2 * 3 * . . . * k
            */
            int lotteryOdds = 1;
            for (int i = 1; i <= k; i++)
               lotteryOdds = lotteryOdds * (n - i + 1) / i;

            odds[n][k] = lotteryOdds;
         }

      // print triangular array
      for (int[] row : odds)
      {
         for (int odd : row)
            System.out.printf("%4d", odd);
         System.out.println();
      }
   }
}

表示作者很牛逼。

/**
   @version 1.20 2004-02-10
   @author Cay Horstmann
*/
package javaDemo;
import java.util.*;

public class LotteryDrawing
{
   public static void main(String[] args)
   {
      Scanner in = new Scanner(System.in);

      System.out.print("How many numbers do you need to draw? ");
      int k = in.nextInt();

      System.out.print("What is the highest number you can draw? ");
      int n = in.nextInt();

      // fill an array with numbers 1 2 3 . . . n
      int[] numbers = new int[n];  //定义一维数组
      for (int i = 0; i < numbers.length; i++)
         numbers[i] = i + 1;//赋值

      // draw k numbers and put them into a second array
      int[] result = new int[k];
      for (int i = 0; i < result.length; i++)
      {
         // make a random index between 0 and n - 1
         int r = (int) (Math.random() * n); //直接使用Math的random方法

         // pick the element at the random location
         result[i] = numbers[r];

         // move the last element into the random location
         numbers[r] = numbers[n - 1];
         n--;
      }

      // print the sorted array
      Arrays.sort(result); //排序数组
      System.out.println("Bet the following combination. It'll make you rich!");
      for (int r : result)
         System.out.println(r);
   }
}